CVE-2026-43027: Linux Kernel use-after-free in Netfilter nf_conntrack_helper

CVE-2026-43027 · Severity: high · CVSS 7.8 · Published 2026-05-01

A vulnerability exists in the Linux kernel's networking subsystem (Netfilter) that could allow a local user to crash the system or potentially execute unauthorized code. The issue occurs when the system fails to properly clean up internal tracking data when a network helper component is removed. This can lead to a 'use-after-free' condition, impacting the stability and security of servers and embedded devices using affected versions of the Linux kernel.

Technologies: Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP. Vendors: Linux, Siemens.

Quick answers

Is CVE-2026-43027 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-43027 being exploited in the wild.
How severe is CVE-2026-43027?
High severity, with a CVSS score of 7.8, published 1 May 2026.
Which products and versions are affected?
Linux Kernel Fixed in various stable branches including 5.10.y, 5.15.y, 6.1.y, 6.6.y, 6.8.y; Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6; Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6.
Is there a fix for CVE-2026-43027?
A patch was published on 2026-04-11: Initial patches applied to stable kernel trees. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-43027 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2026-43027?
Check whether you run Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP or Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A use-after-free vulnerability exists in net/netfilter/nf_conntrack_helper.c. The function nf_conntrack_helper_unregister() incorrectly passed a NULL pointer to nf_ct_expect_iterate_destroy() instead of the actual helper pointer. Consequently, expectations associated with the helper were not destroyed during unregistration. When the helper object was subsequently freed by nfnl_cthelper_del(), remaining expectations maintained a dangling pointer to the freed memory. Subsequent access via expectation dumps or packet-driven conntrack initialization triggers the use-after-free. This can be exploited by a local user to cause a kernel panic or potentially achieve arbitrary code execution. Patches have been released for multiple stable Linux kernel branches.

Affected products

  • Linux Linux Kernel Fixed in various stable branches including 5.10.y, 5.15.y, 6.1.y, 6.6.y, 6.8.y
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6

Timeline

  • 2026-05-01: disclosed
  • 2026-04-11: patched: Initial patches applied to stable kernel trees.

References

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